In recent years, there has been a rapid development of a light emitting element using an organic substance for a emission layer, as a self-light emitting display to take the place of a liquid crystal display. As forming processes of the emission layer made up of an organic substance in an organic EL (electroluminescence) element, a method of forming a film by vapor deposition of a low molecula material, as disclosed in the Appl. Phys. Lett. 51(12), 21 Sep. 1987, p. 913, and a method of coating a high molecular material, as disclosed in the Appl. Phys. Lett. 71(1), 7 July (1997), p. 34 have been mainly developed.
As methods of colorizing there are cited a metal mask patterning method mainly used for the low molecular material, and a liquid droplet ejection patterning method mainly used for the high molecular material.
The metal mask patterning method is a method where light emitting materials having different luminescent colors are deposited by vapor deposition on a desired portion corresponding to pixels over the mask of a predetermined pattern to form a film. The liquid droplet ejection patterning method is a comparatively easy method since it can carry out direct patterning on the portion corresponding to the pixel and is drawing attention.
The metal mask patterning method requires to form films by pattering the organic layers which emit lights in blue (B), green (G) and red (R). However, since it is very difficult to form this organic layer by patterning such as etching or other method after formation of the film, a method where the layers are stacked sequentially by vapor deposition on a first pixel electrode through a vapor deposition mask having a desired pattern is employed. However, this method uses dedicated masks for light emitting organic layers of B, G and R colors for the purpose of preventing contaminations. This involves complicated alignment work. Further, this method requires a troublesome positioning and at the same time it is not effective in improving productivity because of sheet handling process.
In the liquid droplet ejection patterning method, on the other hand, the liquid droplet ejection apparatus is provided with a plurality of liquid droplet ejection heads for ejecting liquid droplets wherein these liquid droplet ejection heads are arranged at uniform pitches to form a group of heads. The head group scans a substrate in the direction of scanning, and ejects liquid droplets at the same time, whereby the liquid droplets of B, G and R colors are ejected onto the substrate. The position of the substrate perpendicular to a scanning direction is adjusted by moving a mount for carrying the substrate. In this method, however, the liquid droplet ejection apparatus scans the substrate which may be contaminated by the operation of the liquid droplet ejection apparatus. Further, as disclosed in the Unexamined Japanese Patent Application Publication No. 2003-251247, sheet handling processing is mostly performed while the substrate is being fixed, and this will not enhance the productivity.
One of the methods proposed to solve the problem of productivity is to create an organic electroluminescence element by forming a functional film on the substrates being conveyed successively.
For example, a technique has been proposed to coat the whole surface of the substrate by bringing a coating solution in contract with the substrate while conveying it (Patent Document 1). This technique may be effective in forming a film on the whole surface of the substrate such as a common functional layer of organic electroluminescence, but is not applicable to the patterning of the B, G and R light emitting layers.
There is disclosed another technique to coat the B, G and R emission layer s in a shape of stripes through a buffer solution (Patent Document 2). This document shows that intermittent formation in a dotted form is also acceptable. However, to cope with patterning on the pixel electrode formed by the arrangement of deltas and mosaic structures, it is necessary to provide three outlets for the B, G and R emission layer s and two outlets for buffer solutions for each pixel. This is not practicably possible. This method has been found to be applicable only to the patterning of the pixel electrode of stripe arrangement in practice.
As described above, the conventional emission layer patterning method is mainly based on the method of sheet processing with the substrate placed at a fixed position, and this arrangement involves productivity problems. At the same time, in the continuous processing mode wherein substrates are conveyed on a continuous basis, there is found no conventional technique capable of achieving the precision patterning of the emission layer.    Patent Document 1: Unexamined Japanese Patent Application Publication No. 2001-6875    Patent Document 2: Unexamined Japanese Patent Application Publication No. 2001-267068